As an important component of a communication system, such as a base station and a repeater station, stability of a radio frequency module directly affects stability of the whole communication system. With the rapid development of communication industry, demand for such stability is increasing. Especially in 3G era, for pursuing higher data rate and spectrum efficiency, linear modulation methods (e.g. QPSK, 16QAM, etc.) are generally employed, and radio frequency modules with higher linearity reliability are needed by such modulation methods. The existing radio frequency modules have defects such as poor gain stability and linearity changeable with temperature due to various reasons.
FIG. 1 is a structural diagram of an existing radio frequency module. As shown in the figure, the radio frequency module comprises a signal input end 11, a power amplification circuit 12, a hardware compensation circuit 13, a monitoring signal line 14, a signal output end 15, a monitoring port 16, a monitoring signal line 17 and a radio frequency shielding housing 19.
Above mentioned existing radio frequency module has following defects:
1. Radio frequency module was designed according to a certain quota of gain and output power, when performance of the power amplifier declines, gain of the radio frequency module declines and output power of the radio frequency module becomes insufficient. Such phenomenon is one of the common problems in current communication devices. Such problem results in unrecoverable decline in performance index of the radio frequency module and the severe ones even result in abnormal operation of the whole communication equipment.
2. Hardware compensation circuit 13 of the radio frequency module uses hardware compensation, that is, uses temperature characteristics of the electronic components themselves for the compensation. Hardware compensation is mainly adjusting gate voltage of the power amplifier. The content of the compensation comprise gain and linearity of the radio frequency module. In practical operations, due to the differences in temperature characteristics among each power amplifiers, as well as differences in temperature characteristics within each electronic component itself, accuracy and reliability of compensated gain and linearity will be lower. Meanwhile, as the gain and linearity are realized by adjusting gate voltage of the power amplifier, in the case of being unable to take both into account, gain compensation and linearity compensation can not meet the need of the radio frequency module in certain extend. For example, gain and linearity compensation circuit in hardware compensation circuit 13 uses hardware compensation, when temperature characteristics of electronic components used in the hardware compensation can not perfectly match characteristics of the power amplifier needed to be compensated, phenomenon of gain and linearity compensation error will present at different temperatures.
3. Parts, in need of circuit compensation, of detection signal and control signal in power amplification circuit of the radio frequency module also commonly use hardware compensation method. For example, downlink output power detection of link in the radio frequency module uses commonly used radio frequency demodulation device, when demodulation curve of the frequency demodulation device differs from compensation curve of demodulation compensation device, phenomenon of inaccuracy downlink output power presents. In practical operations, demodulation curve of the frequency demodulation device often differs from compensation curve of demodulation compensation device, which results in that power detection accuracy for current radio frequency module is not very high with a general error of ±2 dB. When compensation curve seriously differs from demodulation curve, detected error even reaches up to ±5 dB.
4. As shown in FIG. 1, monitoring semaphore of current radio frequency module is directly connected out of control circuit/detection circuit of the module, and gathered to monitoring port 16. Since these monitoring signals are signals of TTL, CMOS or analog that easy to interfere with each other or be interfered by environment, thus influence the performance of radio frequency module.
From these defects existing in prior art, we can see that it is necessary to design a novel compensation method for radio frequency module performance, as well as corresponding radio frequency module, so as to improve accuracy, reliability and anti-interference ability of gain compensation.